Dried singulated cellulose pulp fibers are desirable for many products from absorbent personal articles to a reinforcer in concrete. Currently, in the most common process of making singulated fibers, a roll of conventional pulp fibers is hammermilled into singulated fibers. This process is energy and time intensive, requiring many steps and pieces of processing equipment. Each piece of processing equipment requires a significant capital expenditure and occupies valuable factory floor space. Further, the current hammermilling process often produces fibers with undesirable physical properties, such as low kink, curl, and twist.
This dry singulated pulp will also contain knots of fiber, sometimes referred to as nits or nodules. Knots are fiber clumps that remain strongly adhered to one another as can be seen by placing a small portion of pulp into a clear beaker of water and stirring the water to mix the fibers. Most of the fiber will mix into the water as singular fibers, however there will be fiber clumps that are readily visible. The fiber clumps or knots are undesirable by-products of the hammermilling process. The amount of knots in a pulp that has been hammermilled can be quantified by using a screening system with acoustical energy used as the means to classify the fiber into amounts of knots, accepts and fines. It is desirable to have low knots and fines and high accepts where the accepts are the singulated fibers.
Canadian Patent No. 993618 (Estes, 1976) describes a process for producing a low density fluff pad or batt from individual fibers that have significant kink and interlocking to provide improved batt strength and higher bulk. In accordance with the process, wet pulp is separated into individual fibers during the drying stage. The process uses fluid jet drying equipment that employs air-jets or steam-jets for separating the fibers. The fibers are laid on a perforated screen upon exiting from the jet drier. The process of the Canadian patent produces a mat of interlocked fibers.
Crosslinked fibers are conventionally produced by wetting an already dried roll of conventional pulp fibers with a solution containing a crosslinker prior to hammermilling. The hammermilled pulp containing a crosslinker is then run through a flash drier and further heated in an oven to complete the crosslinking process. This crosslinked pulp has a knot content that is greater than 15%. It is desirable to have a lower amount of knots in crosslinked pulp. Also this conventional process is energy intensive and therefore expensive because the pulp is dried before it is rolled, then hammermilled in wet form with crosslinker, then dried again.
Flash drier systems have been used to directly dry dewatered never dried pulp. The use of flash driers to directly dry dewatered never dried pulp, however, produces a dried pulp with a high amount of knots. Typical knot amounts for flash drying of never dried pulps are 30–40%. Crosslinker containing pulp dried in this manner also results in a knot content similar to or exceeding this level. An overview of a commercial flash drier, the Flakt Flash Drier, and typical flash drier equipment installation is provided by Larsson and Lindstrom, 1996 (“Recent Developments in Pulp Drying”, Larson, O; Lindstrom, B, The World of Pulp and Paper Week, 5th International Conference on New Available Techniques, Jun. 4–7, 1996, Stockholm, Sweden).